The present invention generally relates to the transformation of graphic and video data from VGA to TV interface, and more particularly, to a background-based adaptive method and apparatus for reducing flicker in a picture due to the transformation and improving the quality of the picture.
The transformation of data from a VGA format to a TV format has been necessary in many applications in recent years. The data in a VGA system usually has a progressive scan format. In a TV system, however, the data is normally interlaced. Because of the different data format, flicker phenomenon appears inevitably when VGA data is transformed to TV data if the adjacent scanning lines have large difference. It is very important to reduce the flicker caused by the transformation. Conventional approaches to reducing the flicker often sacrifice the vertical resolution and sharpness of edges in a picture.
Traditionally, the picture of VGA data for computers includes only graphic information. Due to the popularity of DVD (digital video disk), the picture of VGA data comprises both graphic and video information. Generally speaking, graphic data have more high frequency components from a spectral point of view. The change of luminance level is also larger. Therefore, the flicker problem is more pronounced. On the other hand, video data have more low frequency components and the change of luminance level is smaller. It is not so critical whether the flicker problem is addressed or not.
Conventional approaches to flicker reduction do not take into account the content or correlation in the data of a picture. In order to reduce the flicker problem, the whole picture is processed by a flicker reduction algorithm that may also result in picture blurring.
To overcome the drawbacks and improve the quality of a picture, some adaptive techniques, for example, U.S. Pat. No. 5,894,330, have been adopted. Nevertheless, there is a very important issue that is often ignored, i.e., the impact of the background of a picture to a human eye. Because of the ocular property, human eyes are very sensitive to the background of the high luminance level that makes the flicker effect more conspicuous. It is highly desirable to have a flicker reduction technique that can be adaptive to the background and does not sacrifice the quality of a picture.
To overcome the aforementioned drawbacks, the primary object of the present invention is to provide a method for reducing the flicker phenomenon in VGA to TV data transformation by using a background-based adaptive flicker reduction technique. According to this invention, the component of a picture are categorized as cursor, graphic, video data and sub-picture. Except for video data, other components are usually treated as graphic data. In order to improve the resolution of a picture, flicker reduction is only applied to graphic data because video data do not have severe flicker phenomenon in the data transformation.
Another object of the invention is to provide a background-based flicker reduction algorithm that adapts to the background automatically. When the background-based adaptive flicker reduction is enabled, whether the background is bright or dark is determined by computing the mean value around a current pixel. A difference value defined according to the absolute differences between the current pixel and its upper pixel and lower pixel is also computed. The mean and difference values are used to determine how the background-based adaptive flicker reduction method is applied. Four different degrees of flicker reduction which are strong, median, mild and no reduction may be applied.
If the background is bright and the contrast is large around the current pixel, strong flicker reduction is adopted because the flicker phenomenon is very sensitive to the human eye under this circumstance. However, if the background is dark and the contrast is small around the current pixel, flicker reduction is not applied in order to improve the resolution of picture.
A further object of the invention is to provide an easily realizable apparatus for the background-based flicker reduction. According to this invention, the background-based adaptive flicker reduction method can be implemented using simple hardware. Only shifters and simple circuits are required to realize the flicker reduction method. Therefore, the cost of the apparatus for the background-based adaptive flicker reduction of the present invention is relatively low.
These and other objects and advantages of the present invention will become more apparent from a consideration of the following detailed description of preferred embodiments thereof, when read in conjunction with the accompanying drawings.